Detect snprintf && _snprintf, use _snprintf on stupid platforms
(windows).

diff --git a/configure.ac b/configure.ac
index 5fb801b..6bd8b7b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -857,6 +857,7 @@
 	_lwp_create \
 	_pclose \
 	_popen \
+	_snprintf \
 	_stricmp \
 	_strnicmp \
 	chsize \
@@ -887,6 +888,7 @@
 	sendmsg \
 	settimeofday \
 	sigaltstack \
+	snprintf \
 	statfs \
 	strcasecmp \
 	strerror \